It is midsummer. The mowers are active in the field beyond a row of trees. A child who has been clearing the hay props her rake against a tree, doffs a shabby straw hat decorated with meadow flowers, and slumps onto the grass. She leans forward to engage the viewer. In this moment of respite, the sunlight, broken and scattered through overhead foliage, strikes her sleeve, the edge of her skirt and the side of her brow. And this is all there is – save for the fact that the condensing of numerous preparations are distilled in the picture, not to mention the arguments waged in parliament and the press about the proper place for a country child, whether in the schoolroom, or borne on an inexorable tide to the industrial metropolis, or, as here, leading a labourer's life in the open air.

In 1897, George Clausen returned to a painting he had begun several years before, in a moment of upheaval. Six years earlier, he had been looking for a new house and new inspiration. The rural naturalism he had pioneered with works like The Girl at the Gate had reached its limit, and with the unexpected purchase of the painting by the Trustees of the Chantrey Bequest for the National Collection, it seemed as though the battles for what Clausen called 'modern realism' were won. As often occurs in moments of success, he hesitated and took stock, looking back to that heroic decision in 1881 when he and his wife decided to leave London and live in the country. Seeing fieldworkers doing 'simple things under good conditions of lighting', had been a 'liberation', even though, as he later wrote, 'nothing was made easy for you: you had to dig out what you wanted'.

The move had been prompted by the need to reconnect art with real life. Living in the slipstream of the Pre-Raphaelites, there was no point in repeating the mediaeval romances of Millais, Rossetti and Burne-Jones, as others were doing. However, in Paris there was a new movement that was all for naturalistic representation of contemporary conditions, whether in field or faubourg, and the hero of the hour was a young painter, just four years older than Clausen: Jules Bastien-Lepage. This artist had taken the innovations of the Impressionists and applied them in the fields around his home village. His message – that one should seek out one's own coin de terre or 'corner of the earth' – was inspiring many young artists to quit the city for the more primitive life of the fields and fishing ports on the Breton coast.

Clausen was one of their number. In 1882, he travelled to join an artists' colony in the picturesque Breton town of Quimperlé. His time there was brief and he painted only two known works, the Victoria and Albert Museum's Peasant Girl carrying a Jar and A Peasant Girl of Quimperlé, which Bonhams has recently rediscovered and is offering at the 19th Century European, Victorian & British Impressionist Art auction in London in September. One might think of this as a portrait like any other, were it not for the fact that the unidentified model addresses us directly and in a way that is almost challenging. Others would be coy, would trap the viewer in furtive 'come hither' glances, but this young girl is presented as she is, unadorned, in an even, open-air light. Clausen's approach, eschewing artifice, was that of the cool recorder.

After little more than a month, Clausen left Brittany to study at the Académie Julian in Paris. This also lasted no more than a few weeks. Ten years into his career, it was more about checking what others were doing than returning to student life. By December 1882, he was back on the Childwickbury estate, cracking the ice under foot and sketching local labourers preparing winter feed for a flock of sheep. Clausen's entire production was now given over to representing the life of the fields.

If there was a message in this, it was that of social reformers attacking primitive working conditions, promoting agricultural unions, or lobbying for the compulsory education of country children – playing against a backdrop of observations by authors such as Thomas Hardy whose essay on 'The Dorsetshire Labourer' characterised the 'English Hodge' as 'degraded' and 'uncouth'. Although life was hard for labourers' children, there were moments of respite for the chosen few, when posing for an artist must have seemed like a lucrative and undemanding alternative. However, in just over a year, a change of landlord meant that Clausen was looking for another house, followed by a permanent move in 1885 to Cookham Dean in Berkshire.

At the same time, his objective reporting continued to raise concerns among contemporary newspaper critics who were wedded to the literary formulae of the Pre-Raphaelites. The alliance with French art was highly suspect – it was actively undermining what were perceived as stable British traditions. Scandal broke when Clausen and like-minded contemporaries, as members of the New English Art Club, tried to upstage the Royal Academy by organising their own exhibition in April 1886. Battle lines were drawn and factions within the avant-garde – the Newlyn School and the Glasgow Boys – began to emerge.

Clausen was in the middle of a maelstrom, but owed no allegiances. A growing family and good country models in Polly Baldwin, who posed for The Girl at the Gate, and little Rose Grimsdale, who sat for the early studies for Noon in the Hayfield, kept his feet on the ground. Working with Rose sitting at the edge of a field, he began studies that would emerge as a major work. Like most important compositions this began with notes in a sketchbook. Preparatory drawings, pastels and an oil sketch led him to a finished watercolour entitled Idleness, but this occurred when his current lease was coming to an end in 1891, and another move was necessary. Setting up home, finding new motifs and establishing a separate studio at Widdington in Essex delayed its completion. Only with the assistance of a new model, Emmy Wright, was Noon in the Hayfield eventually resumed.

The intervening years had been ones in which Clausen fully embraced Impressionism. His palette was now richer, and he no longer hoped for grey days in which the light would be consistent. With The Girl at the Gate, he realised that he had been 'facing a dead wall' but, as he told the writer George Moore, and as is clear from Noon in the Hayfield, 'a change has taken place...'. It was one that would take him forward to magisterial compositions such as the 'harvest' sequence of 1901-1904 and the dappled shade that envelops the heroic labourers in Building a Rick (1907).

In an interview, Clausen spoke of the difficulties of painting en plein air. Quoting Manet's dictum, that 'in a picture the principal person is the light', he would confess that working under trees, when the patches of sunlight were constantly changing, had its difficulties. He might wait a year or more for the right conditions to return. Other challenges lay ahead in a career that spanned an incredible 70 years, but little would surpass those midsummer days at the end of the 19th century, when men with scythes strike out into a hayfield and a young girl removes her hat and sinks in the shade for her noonday rest.

Kenneth McConkey is Emeritus Professor of Art History at Northumbria University. His book, George Clausen and the Picture of English Rural Life, was published in 2012 by Atelier Books.